Potato Soup
3 potatoes 1 1/2 teaspoons salt 1 quart milk 1/4 teaspoon celery salt 2 slices onion 1/8 teaspoon pepper 3 tablespoons butter Few grains cayenne 2 tablespoons flour 1 teaspoon chopped parsley Cook potatoes in boiling salted water; when soft, rub through a strainer. There should be two cups. Scald milk with onion, remove onion, and add milk slowly to potatoes. Melt half the butter, add dry ingredients, stir until well mixed, then stir into hot soup; boil one minute, strain, add remaining butter, and sprinkle with parsley.
A plain milk-based potato soup thickened with a butter-and-flour roux, in the style of the Boston Cooking School. The proportions are exact enough to follow as written; only a few of the instructions need translating.
- Potato quantity"3 potatoes" assumes medium boiling potatoes of roughly 5-6 oz each. Trust the recipe's own check instead: you want two cups of sieved potato, or about 1 lb 2 oz raw.
- Rubbing through a strainerA ricer or food mill does this in seconds and gives a smoother result than a sieve and spoon. Avoid a blender or food processor, which turns cooked potato gluey.
- Scalding the milkBring the quart of milk just to the point where bubbles form at the edge and steam rises, around 180F. This is for flavour extraction from the onion, not sterilisation; do not let it boil over.
- "Add dry ingredients"This means the flour, salt, celery salt, pepper and cayenne, stirred into the melted butter to make a seasoned roux. The parsley and the second half of the butter are held back to the end.
- The one-minute boilFlour needs that brief boil to lose its raw taste and set its thickening. Longer boiling of a milk soup risks scorching on the bottom of the pan, so use a heavy pot and stir constantly.
- Straining at the endThe final strain catches any lumps of roux and stray potato fibre. If your roux went in smoothly you can skip it, though the soup will be a shade less silky.
- Celery saltStill sold, but modern blends vary in strength and salt content. Add the 1 1/2 teaspoons of plain salt first, then the celery salt, and taste before the last of it goes in.
- YieldRoughly five to six cups, serving four to six as a first course. It thickens noticeably as it cools; thin with a little hot milk when reheating, over low heat.
Potato soup of this kind belongs to the late nineteenth-century American cooking-school tradition, which standardised household cookery into level measurements and repeatable formulas. The structure here is a familiar one from those books: a starchy vegetable puree, scalded milk infused with onion, and a butter-and-flour binding, the same skeleton used for other cream soups such as cream of celery and cream of pea. The teaspoon of chopped parsley at the end is a period touch, adding colour to a pale soup.